6a.6 Inter‑UE Transfer without establishing a Collaborative Session

23.2373GPPIP Multimedia Subsystem (IMS) Service ContinuityRelease 17Stage 2TS

6a.6.1 Inter-UE Transfer initiated by the source UE

UE-1 and UE-2 are under the same user subscription. UE-1 is involved in IMS session with remote party. The information flow in Figure 6a.6.1-1 shows transfer of the session from UE-1 to UE-2. Since the entire session is transferred simultaneously, the roles of the Controller UE and Controllee UE are not applicable.

NOTE 1: This signalling flow does not require the UE-2 to have IUT capabilities.

Figure 6a.6.1-1: Inter‑UE transfer without establishing Collaborative Session – initiated by the source UE

1. UE-1 sends IUT media and service control transfer request to the SCC AS to transfer the session that includes Media-A from UE-1 to UE-2. The IUT media and service control transfer request shall include enough information for the network to:

– identify the transferred session;

– identify that the target of the transferred session is UE-2;

– identify the access leg of UE-1 to be transferred to UE-2.

2. If the SCC AS does not have the list of Public User Identities that share the service profile with the Public User Identity used by UE-1 for the Collaborative Session, the SCC AS retrieves this information. If the Collaborative Session Control transfer request indicates that UE-2 has the same Public User Identity (but different public GRUU) as UE-1, this step is skipped.

3. The SCC AS ensures that the Public User Identity used by UE-2 shares the service profile with the Public User Identity used by UE-1 for the Collaborative Session. The SCC AS performs authorization as specified in clause 6a.12, then initiates the media session setup procedure with UE-2 for the Media-A, and updates the Remote Party.

4. The SCC AS releases the session with UE-1.

When the above transfer is completed the SCC AS retains the service state (e.g. media flows status) of UE-2, and the UE-2 has the control of the IMS session.

NOTE 2: If, besides the Media-A, there are other media flows in an unrelated session between UE-1 and Remote Party, the other media flows are not impacted by the above session transfer operation.

6a.6.2 Inter-UE Transfer initiated by the target UE

UE-1 and UE-2 are under the same IMS subscription. UE-1 is involved in IMS session with remote party. Figure 6a.6.2-1 shows session transfer from UE-1 to UE-2 requested by UE-2. Since all the media flow(s) are transferred from UE-1 to UE-2 simultaneously, the roles of the Controller UE and the Controllee UE are not applicable.

Figure 6a.6.2-1: Inter UE Transfer initiated by UE not participating in the session – no Collaborative Session established

1. UE-2 obtains information about the existing sessions and their media flows.

2. UE-2 sends IUT media and service control transfer request. The request shall include enough information for the network to:

– identify the transferred session;

– identify that the target of the transferred session is UE-2;

– identify the access leg of UE-1 to be transferred to UE-2.

3. If the SCC AS does not have the list of Public User Identities that share the service profile with the Public User Identity used by UE-1 for the Collaborative Session, the SCC AS retrieves this information. If the Collaborative Session Control transfer request indicates that UE-2 has the same Public User Identity (but different public GRUU) as UE-1, this step is skipped.

4. The SCC AS ensures that the Public User Identity used by UE-1 shares the service profile with the Public User Identity used by UE-2 for the Collaborative Session. The SCC AS performs authorization as specified in clause 6a.12; in particular, the SCC AS requests the UE-1 to authorize the pull request or the SCC AS authorizes the request on behalf of UE-1 (e.g. pre-configured). The SCC AS will also authorize that the target UE is of the same subscription. If the request is authorized, SCC AS continues in accordance with step 2 of clause 6a.6.1, i.e. SCC AS establishes a session with UE-2 for the Media-A, removes Media-A from UE-1, and updates Remote Leg using the Remote Leg Update procedure.

5. The SCC AS sends IUT media and service control transfer response to UE-2.